a) Field of the Present Invention
The present invention relates to an encoder used for various motors and a parameter establishing device capable of establishing various bits of parameter information for the encoder from the outside of the encoder.
b) Description of the Related Art
As shown in FIG. 8, a conventional servo motor comprises, for example, brushless motor 41, encoder 45, which separately detects data on a rotational position of brushless motor 41 and data on an absolute position of the motor's magnetic poles, and control device 42 which controls the driving of brushless motor 41 according to a detection signal from encoder 45. Also, cables are used for transmission of signals between encoder 45 and control device 42.
Encoder 45 is stored in case 50 as shown in FIG. 8 (indicated with a dotted line to avoid making the figure busy) wherein disc-shaped pole detecting magnet 46 is formed at the end of main shaft 41 a of brushless motor 41. Pole detecting magnet 46 transmits driving position data in association with U, V and W phases; also, it is magnetized in such a way that N and S poles, which are equivalent of magnetic poles of brushless motor 41, alternate around the circumference. In addition, drum-shaped magnetic recording medium 47 is formed between pole detecting magnet 46 and brushless motor 41. Magnetic recording medium 47 transmits rotational position data in association with Z, A and B phases; also, it consists of an upper portion, which is magnetized in such a way that a pair of N and S poles is positioned adjacent to each other at a position on the circumference, and a lower portion which is magnetized in such a way that N and S poles alternate around the circumference.
Furthermore, a plurality of Hall devices 45a and MR sensor 45b are positioned across from the magnetized areas of pole detecting magnet 46 and magnetic recording medium 47, respectively. Hall devices 45a are mounted on the reverse side of signal processor base 17 on which an encoder internal signal processor circuit is formed.
Hall devices 45a and MR sensor 45b generate pulses caused by rotation of brushless motor 41. Also, encoder 45 and control device 42 are connected to each other via cables such that control device 42 controls the driving of brushless motor 41 by using pulses from encoder 45.
In this case, brushless motor 41 can be of various modes; for example, ones with 50 W, 100 W to 1.1 kW and ones having two pairs or one pair of N and S poles of magnets. Also, depending on the use, encoder 45 itself can be such that 500 pulses or 1,000 pulses per rotation can be generated. Therefore, various combinations of brushless motor 41 and encoder 45 are possible.
However, conventional encoder 45 does not have a function to determine what kind of encoder shall be used according to kind of the brushless motor, that is, a self-diagnosing function. Hence, various parameters must be established during manufacturing of the encoder. Examples of such various bits of parameter information include the number of magnetic poles of brushless motor 41, the code indicating intensity of brushless motor 41 in watts, an identification number (ID) of encoder 45, codes indicating the manufacturing number, model, manufacturer and manufacturing date of encoder 45, codes assigning the number pulses per rotation in association with A and B phases of encoder 45, and a transmission format. The above various bits of parameter information are established on signal processor base 17 by a short pin or a dip switch; after the information is established, the cover of case 50 is closed.
Nonetheless, transmission of signals from encoder 45 and control device 42 in the above conventional servo motor is one-way transmission in which only output from encoder 45 to control device 42 is constantly generated. As a result, once the cover of case 50 of encoder 45 is closed after various bits of parameter information are established, the information in encoder 45 cannot be changed. Therefore, if there is a mistake in the selection of signal processor base 17 in encoder 45 or a mistake in the established parameter information, replacement of signal processor base 17 and reestablishment of the mistaken parameter information must be carried out by reopening the cover. This causes undesirable operations such that the cost of the servo motor is increased.